JavaScriptCore-1097.3.tar.gz

[apple/javascriptcore.git] / dfg / DFGRedundantPhiEliminationPhase.cpp

diff --git a/dfg/DFGRedundantPhiEliminationPhase.cpp b/dfg/DFGRedundantPhiEliminationPhase.cpp
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+/*
+ * Copyright (C) 2012 Intel Corporation. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ */
+
+#include "config.h"
+#include "DFGRedundantPhiEliminationPhase.h"
+
+#if ENABLE(DFG_JIT)
+
+#include "DFGGraph.h"
+
+namespace JSC { namespace DFG {
+
+class RedundantPhiEliminationPhase : public Phase {
+public:
+    RedundantPhiEliminationPhase(Graph& graph)
+        : Phase(graph, "redundant phi elimination")
+    {
+    }
+    
+    void run()
+    {
+        bool changed = false;
+        do {
+            changed = fixupPhis();
+        } while (changed);
+
+        updateBlockVariableInformation();
+
+        // Update the Phi references from non-Phi nodes, e.g., the GetLocals.
+        for (NodeIndex index = 0; index < m_graph.size(); ++index) {
+            Node& node = m_graph[index];
+
+            if (!node.shouldGenerate())
+                continue;
+
+            switch (node.op()) {
+            case GetLocal:
+                replacePhiChild(node, 0);
+                break;
+            default:
+                break;
+            }
+        }
+
+    }
+
+private:
+    NodeIndex getRedundantReplacement(NodeIndex phi)
+    {
+        NodeIndex child1 = m_graph[phi].child1().indexUnchecked();
+        NodeIndex candidate = child1 == phi ? NoNode : child1;
+
+        NodeIndex child2 = m_graph[phi].child2().indexUnchecked();
+        if (candidate != NoNode) {
+            if (child2 != NoNode && child2 != candidate && child2 != phi)
+                return NoNode;
+        } else if (child2 != phi)
+            candidate = child2;
+
+        NodeIndex child3 = m_graph[phi].child3().indexUnchecked();
+        if (candidate != NoNode) {
+            if (child3 != NoNode && child3 != candidate && child3 != phi)
+                return NoNode;
+        } else if (child3 != phi)
+            candidate = child3;
+        
+        return candidate;
+    }
+
+    bool replacePhiChild(Node& node, unsigned childIndex)
+    {
+        ASSERT(childIndex < 3);
+
+        bool replaced = false;
+        NodeIndex child = node.children.child(childIndex).indexUnchecked();
+        if (child != NoNode && m_graph[child].op() == Phi) {
+            NodeIndex childReplacement = getRedundantReplacement(child);
+            if (childReplacement != NoNode) {
+                node.children.child(childIndex).setIndex(childReplacement);
+                replaced = true;
+                if (node.refCount()) {
+                    m_graph[childReplacement].ref();
+                    m_graph.deref(child);
+                }
+            }
+        }
+        return replaced;
+    }
+
+    bool fixupPhis()
+    {
+        bool changed = false;
+
+        for (BlockIndex block = 0; block < m_graph.m_blocks.size(); ++block) {
+            Vector<NodeIndex>& phis = m_graph.m_blocks[block]->phis;
+
+            for (size_t i = 0; i < phis.size(); ++i) {
+                NodeIndex phi = phis[i];
+                Node& phiNode = m_graph[phi];
+
+                changed |= (replacePhiChild(phiNode, 0) && phiNode.refCount());
+                changed |= (replacePhiChild(phiNode, 1) && phiNode.refCount());
+                changed |= (replacePhiChild(phiNode, 2) && phiNode.refCount());
+            }
+        }
+
+        return changed;
+    }
+
+    void updateBlockVariableInformation()
+    {
+        // Redundant Phi nodes are eliminated, we need to update
+        // the variable information if it references them.
+        for (BlockIndex blockIndex = 0; blockIndex < m_graph.m_blocks.size(); ++blockIndex) {
+            BasicBlock* basicBlock = m_graph.m_blocks[blockIndex].get();
+
+            for (size_t arg = 0; arg < basicBlock->variablesAtHead.numberOfArguments(); ++arg) {
+                NodeIndex nodeIndex = basicBlock->variablesAtHead.argument(arg);
+                if (nodeIndex != NoNode && m_graph[nodeIndex].op() == Phi && !m_graph[nodeIndex].refCount()) {
+                    NodeIndex replacement = getRedundantReplacement(nodeIndex);
+                    if (replacement != NoNode) {
+                        // This argument must be unused in this block.
+                        ASSERT(basicBlock->variablesAtTail.argument(arg) == nodeIndex);
+                        basicBlock->variablesAtHead.argument(arg) = replacement;
+                        basicBlock->variablesAtTail.argument(arg) = replacement;
+                    }
+                }
+            }
+
+            for (size_t local = 0; local < basicBlock->variablesAtHead.numberOfLocals(); ++local) {
+                NodeIndex nodeIndex = basicBlock->variablesAtHead.local(local);
+                if (nodeIndex != NoNode && m_graph[nodeIndex].op() == Phi && !m_graph[nodeIndex].refCount()) {
+                    NodeIndex replacement = getRedundantReplacement(nodeIndex);
+                    if (replacement != NoNode) {
+                        // This local variable must be unused in this block.
+                        ASSERT(basicBlock->variablesAtTail.local(local) == nodeIndex);
+                        basicBlock->variablesAtHead.local(local) = replacement;
+                        basicBlock->variablesAtTail.local(local) = replacement;
+                    }
+                }
+            }
+        }
+    }
+
+};
+
+void performRedundantPhiElimination(Graph& graph)
+{
+    runPhase<RedundantPhiEliminationPhase>(graph);
+}
+
+} } // namespace JSC::DFG
+
+#endif // ENABLE(DFG_JIT)